Flattener uneven correction on FF camera

Equipment Flattener Refractors
12 replies•431 views
Didier Kobi avatar
Didier Kobi avatar
Hi all,

I have juste received a 0.8x flattener for my new 360mm refractor (the 1x flattener is still on backorder :/ ) and I was not expecting stellar result as the flattener is made for APS-C and I have a FF (corrected field is 33mm vs 43mm for my sensor diagonal).

However, on the image below (forget the vignette: did use flats made without a corrector) it seems pretty obvious that the correction is far worst on the right part of the image compared to the left part (even if there are no big star to compare with). Is this an issue related with the tilt of my camera sensor? Or the poor quality of the corrector (TS-Optics).

If it is a tilt issue and considering the flattener has 55mm back focus made for my Canon camera, how could I solve it considering I cannot put a tilt corrector between the 0.8x flattener and the camera sensor? Or do I need to put the corrector between the telescope and the flattener?

Because at this stage, the flattener seems not very useful considering how much I need to crop the photo to get decent result. EDIT: Not useful compared to a 1x flattener.


TIA for your input. 

Engaging
andrea tasselli avatar
andrea tasselli avatar
Hpw do you attach the camera (and what camera) to the flattener/reducer?
Didier Kobi avatar
Didier Kobi avatar
andrea tasselli:
Hpw do you attach the camera (and what camera) to the flattener/reducer?

I have a Canon 5D mk II DSLR attached to the flattener with a M48 T-Ring
Andy Wray avatar
Andy Wray avatar
Do you have an equivalent photo without the flattener?  It would be good to see how much improvement you have with it.
Well Written Respectful Engaging
andrea tasselli avatar
andrea tasselli avatar
Didier Kobi:
andrea tasselli:
Hpw do you attach the camera (and what camera) to the flattener/reducer?

I have a Canon 5D mk II DSLR attached to the flattener with a M48 T-Ring

I'm leaning toward thinking the M48 adapter being the issue, or the way it is attached to the FF. Often times this is the issue n.1.
Didier Kobi avatar
Didier Kobi avatar
I did a test a few days ago with no corrector (left) and here is the equivalent with the 0.8x flattener (right) :

The flattener did actually improve the stars quite a bit, especially near the corners. Without correction, even a crop of the nebula is not usable and it is OK with the flattener, but it would be even better I think if the deformation were even as the bottom of the picture seems quite a bit better. 

Below is the top-left corner.

Didier Kobi avatar
Didier Kobi avatar
andrea tasselli:
I'm leaning toward thinking the M48 adapter being the issue, or the way it is attached to the FF. Often times this is the issue n.1.

Interesting actually.

The photo above with no corrector (left) was done with another M42 T-Ring and the deformation seems more symmetrical: the top and bottom of the photos




If it is the issue what would be the solution? Another M48 adapter? How to know it it would be better?
andrea tasselli avatar
andrea tasselli avatar
The idea is to measure whether the way it is made or secured does not make it tilt. You'd need a micrometer, rather cheap these days if you can't borrow one. Another option would be to use an adjustable coupler, something like this:

https://www.firstlightoptics.com/adapters/astro-essentials-m48-female-to-m42t-male-tilt-adjuster.html

Third option is to make it tilt to oppose the apparent tilt of the focal plane and you'd need shims (0.05 to 0.2 mm) to achieve the required effect but it is, needless to say, tricky.
Didier Kobi avatar
Didier Kobi avatar
andrea tasselli:
The idea is to measure whether the way it is made or secured does not make it tilt. You'd need a micrometer, rather cheap these days if you can't borrow one. Another option would be to use an adjustable coupler, something like this:

https://www.firstlightoptics.com/adapters/astro-essentials-m48-female-to-m42t-male-tilt-adjuster.html

Third option is to make it tilt to oppose the apparent tilt of the focal plane and you'd need shims (0.05 to 0.2 mm) to achieve the required effect but it is, needless to say, tricky.

The adapter seems good and I cannot see anything wrong with the attachment, but obviously I wouldn't notice if the adapter's body was physically not exactly level.

Concerning the tilt adjuster, the problem is that the flattener has 55mm back focus which is exactly what I need with the M48 T-Ring and I don't have the possibility to put anything in-between if I am right. 

And the third option is I think a little bit too tricky for me  

But thanks for your advices!

I guess I can also live with it and maybe correct the stars in PP if needed, but a hw solution would obviously be better.
Torsten Mueller avatar
Torsten Mueller avatar
Hi Didier,
i also think its some sort of tilt, but what exact telescope, adapter and flattener are you using?

Cheers
Torsten
Didier Kobi avatar
Didier Kobi avatar
Torsten Mueller:
Hi Didier,
i also think its some sort of tilt, but what exact telescope, adapter and flattener are you using?

Hi Torsten,

I am using a Tecnosky 360/60 APO telescope and this TS-Optic flattener here

https://www.astromanie.ch/fr/correcteurs-optiques/1417-correcteur-ts-optics-08x-pour-refracteur-ed-et-apo-avec-ouverture-60-a-65-mm.html

However, I have received another 1x flattener since

https://www.pierro-astro.com/tsoptics/correcteur-de-champ-pour-lunettes-ed-et-apo_detail 

Not sure the brand: the page has the WO logo but is in the TSOptic section and the flattener itself has no brand on it :/

I am a bit disappointed by the result on my FF Canon 5D mk II of this 1x flattener (see image below): not really flat even on an APS-C Crop, but the flattener is made for 70-100mm tubes , so I may have too high expectation on a 60mm telescope. The dedicated Tecnosky 1x flattener is still backordered and hopefully it will help me get better corrected photos on my FF.

But the point is that the deformation with this 1x flattener seems symmetrical while it is not with the 0.8x flattener (same M48 T-ring used), so if there is any tilt issue it seems to be linked to the 0.8 flattener itself.

0.8x flattener = asymmetrical deformation


1x flattener = symmetrical deformation
Helpful
Andy Wray avatar
Andy Wray avatar
FWIW:  that 1x field flattener doesn't seem to be helping much at all.  Most sites refer to it as the "OVL field flattener".  I'm guessing this is http://www.opticalvision.co.uk/.  It's a pretty cheap flattener, but even so I would have expected a better result.  It may be worth consulting them.
Didier Kobi avatar
Didier Kobi avatar
Andy Wray:
FWIW:  that 1x field flattener doesn't seem to be helping much at all.  Most sites refer to it as the "OVL field flattener".  I'm guessing this is http://www.opticalvision.co.uk/.  It's a pretty cheap flattener, but even so I would have expected a better result.  It may be worth consulting them.

Thanks for the info! It is better than no flattener, but apparently I was right to be somehow disappointed by it.

It is this one indeed http://www.opticalvision.co.uk/astronomical_accessories-camera_adaptors_and_imaging_products/field_flattener_with_t-ring_adaptor.html 

I did buy it because I couldn't wait for the backordered flattener for my telescope and it was quit cheap indeed, but I guess there is a reason for that.
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